The present invention relates to a variable displacement compressor used in a refrigerant circuit of a vehicle air conditioner. More particularly, the present invention pertains to a control valve that changes the displacement of the compressor based on the pressure in a crank chamber.
Japanese Unexamined Patent Publication No. 11-324930 discloses such a displacement control valve for compressors. As shown in FIG. 7, a valve chamber 101 is defined in a valve housing 105. The valve chamber 101 forms a part of a supply passage 104, which connects a discharge chamber 102 to a crank chamber 103 of a compressor. A valve body 106 is movably located in the valve chamber 101. The opening degree of the supply passage 104 is adjusted in accordance with the position of the valve body 106 in the valve chamber 101. A pressure sensing chamber 107 is defined in the valve housing 105. A pressure sensing member 108, which includes a diaphragm, divides the pressure sensing chamber 107 into a first pressure chamber 109 and a second pressure chamber 110.
Two pressure monitoring points P1, P2 exist in a refrigerant circuit (refrigeration cycle). A first pressure monitoring point P1 is located in a higher pressure zone.
That is, the first pressure monitoring point P1 is exposed to a pressure PdH to which the first pressure chamber 109 is exposed. A second pressure monitoring point P2 is located in a lower pressure zone. That is, the second pressure monitoring point P2 is exposed to a pressure PdL to which the second pressure chamber 110 is exposed. The pressure difference xcex94Pd (xcex94Pd=PdHxe2x88x92PdL) between the first pressure chamber 109 and the second pressure chamber 110 represents the flow rate in the refrigerant circuit. Fluctuations of the pressure difference xcex94Pd, or displacements of the pressure sensing member 108 based on fluctuations of refrigerant flow rate in the refrigeration circuit, affect the position of the valve body 106. Accordingly, the displacement of the compressor is changed to counteract the fluctuations of the refrigerant flow rate.
If the speed of an engine that drives the compressor changes when the compressor displacement is constant, the flow rate of refrigerant in the refrigerant circuit, or the pressure difference xcex94Pd, is changed. The pressure sensing member 108 changes the pressure displacement such that the changes of the pressure difference xcex94Pd are cancelled. Accordingly, the refrigerant flow rate in the refrigerant circuit is maintained.
However, the diaphragm used in the pressure sensing member 108 is costly and difficult to machine. Also, since the circumference of the pressure sensing member 108 must be fixed to the valve housing 105 (the inner wall of the pressure sensing chamber 107), the installation of the pressure sensing member 108 is troublesome, which increases the cost of the control valve.
Accordingly, it is an objective of the present invention to provide a control valve used in a variable displacement compressor having an inexpensive pressure sensing member that is easy to install in a valve housing.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve used for a variable displacement compressor in a refrigerant circuit is provided. The compressor changes the displacement in accordance with the pressure in a crank chamber and includes a supply passage, which connects a discharge pressure zone to the crank chamber, and a bleed passage, which connects a suction pressure zone to the crank chamber. The control valve includes a valve housing, a valve chamber, a valve body, a pressure sensing chamber, a spherical pressure sensing member and first and second pressure monitoring points. The valve chamber is defined in the valve housing and is part of the supply passage or the bleed passage. The valve body is located in the valve chamber and changes its position in the valve chamber thereby adjusting the opening size of the supply passage or the bleed passage in the valve chamber. The pressure sensing chamber is defined in the valve housing. The pressure sensing member is movably located in the pressure sensing chamber and divides the pressure sensing chamber into a first pressure chamber and a second pressure chamber. The first and second pressure monitoring points are located in the refrigerant circuit. The first pressure chamber is exposed to the pressure at the first pressure monitoring point. The second pressure chamber is exposed to the pressure at the second pressure monitoring point. The pressure sensing member moves in accordance with the pressure difference between the first pressure chamber and the second pressure chamber. The position of the valve body is determined based on the position of the pressure sensing member.